Immunize Plants?
Nature Does It. Why Can’t We?

by Paul W. Syltie, Ph.D.

Modern agriculture and horticulture have garnered a vast arsenal of chemicals to fight a never-ending array of fungal, bacterial, viral, insect, and other pests which annually cost production by well over 12%. About $25 billion were spent in 1993 on chemical pesticides, and still the carnage continues. Is there any way out of this quandary ... to control pest without harmful, environmentally polluting chemicals?

As I oftentimes mention, look to nature for the answers. What we find is a complex array of sophisticated mechanisms within plants that defend against microbial and insect invasion. All we need to do is tap into this system already in place and treat our plants as nature does.

How does a plant naturally defend itself? Soybean plants, for example, appear to use a cascade of defenses against an invading fungus (see the diagram, upper right). Within minutes of the attack an initial blockade is formed: the plant begins cross-linking proteins in the cell walls at the invasion site, sort of like closing the slats of a venetian blind to block fungal movement. Then some of the cells around the infection die, surrounding the fungus while releasing acidic and other defensive substances that further frustrate the invader. This is called the hypersensitive response.

After the initial blockade to slow down fungal extension, surrounding cells are given more time to begin producing potent chemicals called phytoalexins. These chemicals can stunt development of the fungal mycelia, much like penicillin does to fungus colonies in a petri dish. A message is somehow sent to more distant cells to produce precursors to antibiotics in case they are needed there. Finally, the whole plant mobilizes to fight the invader. Enzymes called chitinases and glucanases, which can break down the exterior of fungi, are synthesized and disseminated throughout the plant. Parts of the plant far removed from the infection also cross-link their cell walls in case the invader penetrates further (N. Angier, Plants defy microbes with immune defense and self-mutilation, The New York Times, August 18, 1992).

Plants of all types do this sort of thing to defend themselves on a regular basis. It is the sort of thing our own bodies do, though on a somewhat different scale and with obvious differences. Yet, plants can perform some quite amazing feats that we are only beginning to understand. Can these immunization responses of plants be used in a practical way today by farmers and horticulturalist?

These hyphae are the cause of Gaeumannomyces infection, or “take-all” of wheat. Note how bacterial infection has caused the collapse of the hyphae on the right, with a breach created in the wall at the arrow.

The answer is “yes”! Dr. Joseph Kuc at the University of Kentucky has immunized cucumber seedlings against disease using anthracnose fungus. By inoculating seedlings with the fungus to produce a mild infection, the cucumber plants are protected from severe infection for up to six weeks. Later damage is reduced by more than 98%! What is more, the immunized plants were protected from at least 12 other diseases caused not only by fungi, but also bacteria and viruses as well which infest the roots, fruit, and leaves (Stephen Day, A shot in the arm for plants, New Scientist, January, 1993).

Other researchers have similarly studied the inoculation of cotton seedlings with spider mites to increase resistance to wilt; conversely, cotton seedlings infected with the wilt fungus acquire resistance to spider mites. Injecting tobacco plants with aspirin (salicylic acid) protects them against the tobacco mosaic virus. It has recently been found that most plants, in response to necrosis of leaf tissue, produce immunity-enhancing salicylic acid. Other plants respond to insect attack by brandishing more hairs, thorns, or tougher bark, or by producing internal toxins.

We would do well to emulate nature, where natural disease resistance of plants is fostered by excellent nutrition within a soil replete with symbiotic rhizosphere [“root-zone”] bacteria, fungi, algae, cyanobacteria, actinomycetes, protozoa, and other organisms. Ecosystems are naturally complex, with many species of plants inhabiting the same vicinity, their roots intermingling. While our monoculture production systems may not be able to be modified to include a diversity of species in our fields, yet we can utilize proven soil mineral balancing techniques, return lots of organic matter to the soil, minimize tillage, and in other ways encourage the laws of nature to assist in plant immunization. We also can utilize new advances in “systemic acquired resistance” (SAR) by applying immunizing agents to plants, once these methods are available. In essence, we can “turn on” the genes that help the plant resist attack. It is possible that the effect of Vitazyme biostimulant to thwart the development of plant disease may be due in part to enhanced immunity. This enhancement may be through nutritional effects, whereby more of the needed nutrients and co-factors for defense are produced through rizosphere stimulators.

One thing we all can do is raise healthy plants with soils and media well-balanced in the necessary major and minor elements, as well as organic matter. Conforming to the inherent laws of nature will go a long ways towards insuring that plants will express their inherent immunity to resist diseases.